Lethality and kinetic of diatomaceous earth uptake by the bean weevil (Acanthoscelides obtectus [Say] Coleoptera: Bruchinae): Influence of short-term exposure period

摘要

Laboratory bioassays were carried out to assess the lethal effect of the diatomaceous earth (DE) formulation Fossil-Shield (R) against males and females of adult bean weevils (Acanthoscelides obtectus [Say]). Kinetics of the DE uptake experiment was determined by using manganese as a trace element. The adherence of DE to the common bean was also measured in this study. The mortality of weevils was evaluated after exposure to eight different DE dosages (400-4000 mg/kg) after 1, 2 and 4 days, respectively. DE dust was more lethal to male than female weevils within shorter exposure period at low DE dosages (<2400 mg/kg). However, LD99 values did not show a significant difference (P> 0.05) between sexes. DE adherence ratio ranged between 73% and 98% at the highest (3600 mg/kg) and the lowest (400 mg/kg) DE dosages, respectively. The maximum saturated amount of DE retention on the bean surface was approximately 7.14 mu g/mm(2). The amount of DE uptake by a weevil was significantly increased (P < 0.05) with DE dosage and exposure time. The two-compartment kinetic model fitted well to the experimental data as a two-site reaction model over the range of DE dosage between 500 and 2000 mg/kg. According to the model, bean weevils can take-up 2.3-3.1 mu g/mm(2) of DE based on their corresponding LD99 values depends on the exposure period. It was observed that DE particles were incorporated into the epicuticle lipid layer at a rate of 1.18 x 10(-3) mu g mm(-2) min(-1) during DE uptake by a weevil. This indicates that from the total body weight, approximately 2% of DE taken-up by an insect within a given exposure period was more decisive for insect mortality than the rate of DE application. (C) 2019 Elsevier Ltd. All rights reserved.